Here's my (unsolved) use case for a smart home: I've got three heat pumps and a whole house generator; if the generator is on, I don't want all three running at the same time (too much load), and generally, I'd like the set points adjusted, because I value saving fuel (the tank needs to last until the next filling, and I don't know how long the outage will be) over comfort. I've also got a hot water recirculator that I'd like to turn off when the well pump isn't powered (it's not on the same circuit as the house) or is otherwise not providing water pressure --- after a water leak, the previous recirculator burned its bearings moving air instead of water, and it was expensive to replace.

Also, I'd love to run the HVAC fans to equalize temperatures when some rooms are much cooler than others.

This type of scenario shouldn't require "smart" home hardware - Traditionally situations like this were addressed by wired/wireless SCADA networks or BACnet or similar protocols.

The only issue is that these things are typically designed to be engineered along with the systems they control, and are difficult for the average user to implement or use.

The thing is, "smart" home hardware is a lot less expensive and more accessible than SCADA or BACnet. I can go out and buy any number of home thermostats, and some of them are even capable of properly supporting all the functions; unfortunately I ended up with the Nest, because it has the best support for enabling both auxiliary heat and emergency heat; but it doesn't have support for interfacing via LAN, and Google rescinded the APIs. Also, the physical interface is infuriating, but it's better than the awful honeywell touchscreen garbage the previous homeowner had installed.

Assuming all those devices have means to communicate state and receive commands, that would be easy enough to do with Home Assistant.

> I can't even imagine a scenario where I'd want a "smart home".

You get hit by a truck on the way to work and you're not longer able bodied enough to do these things.

Fair enough, but these things aren't marketed as assistive devices.

I have smart lights in the bedroom. They come automatically as a light-alarm and it's fantastic. It would be hard to go back to waking up in the dark and turning on a massively bright light.

It's also remote controlled at night so I can turn it off from bed. These are all useful features.

> It would be hard to go back to waking up in the dark and turning on a massively bright light.

That's why we invented the sun.

I wake up before the sun comes up and go to bed long after it's gone down.

It doesn't have to be "smart" or internet-connected to be remotely operable.

None of it is "necessary", but having my locks, garage doors, HVAC, doorbell[1], most of my media players, and most of my lights integrated with Home Assistant provides all sorts of convenience.

It all works "offline" (in reality, as long as the house has power, it all works, I just can't connect to it if I'm not home).

[1] The doorbell is a "dumb" doorbell that triggers an IO pin on an ESP8266.

Turn on the heating/cooling on your way home from work.

Energising white light in the morning, soft warm lighting in the evening.

Shutters that close when the sun hits them in the summer to reduce the AC bill.

Turn on the dehumidifier if the humidity > 60%

So so many applications. Granted most of this is "nice to have" but this is also why it's not a big deal if it goes down every once in a while.

> Turn on the dehumidifier if the humidity > 60%

Humidifiers with humidity sensors are not “smart” anymore than a furnace hooked up to a thermostat. I got one in 1987 or so.

All of these things can be done without internet connectivity.